Acceleration day one and two

On the first day of acceleration week I began by distributing slips of paper. I asked the students to sketch what they thought the time versus distance graph would be for a RipStik accelerating from rest, going faster and faster. The students had done this the week before when I asked them to predict the graph of time versus distance for a RipStik moving at a constant velocity, a constant speed.

The most common sketch was a linear prediction, the same graph as last week's constant velocity run.

A variation on a linear velocity was the above graph.

This was an interesting prediction. There wasn't the time nor the conditions to determine what the student was thinking.

Of 26 students only three sketched a rising curve. Bear in mind that last week the class rolled a ball at slow, medium, and fast speeds. They learned that slope is speed and that slope increases with increasing speed. This did not translate into better predictions for accelerated motion.

The various predictions were reflected onto the board.

Then a RipStik run was launched from up near the LRC. This was a new start location. Measurements were made at three meter marks "backwards" off of the pre-existing zero meters from the week prior.

A 1.5 meter mark was added. This would prove remarkably propitious on Wednesday.

This converted the former zero line into the 12 meter mark or thereabouts. Then 15 and 18 were on the pre-existing 3 and 6 meter marks.

Data from the run timed by the instructor.

The parabola came true. The acceleration was better in part because new Salomon Genesis GTX shoes provide excellent RipStik board grip. Terminal velocity up around 2.76 meters per second. The new starting location proved worthy. Why hadn't starting upslope been stumbled into before?

Acceleration was 0.21 meters per second squared.

On Wednesday an out and back deceleration to acceleration run was done as in prior terms. The combination of the grip provided by the Salomon Genesis shoes which gave me a higher inbound starting velocity and the 10.5 meter mark (1.5 on Monday - this is a run direction disteng) set up for surprisingly solid data. Again, three timers were used. Students handled all the timing.

10.5 was a reach, but was just barely crossed.

The graph was one of best. The shoes allowed a harder, faster, better acceleration after the 180° turn.

The initial velocity exceeded three meters per second, a high velocity against RipStik runs in the recent past.

The serendipitous marking of 1.5 meters appears to have contributed to a successful Wednesday run and demonstration of a full parabola.